scholarly journals ELECTRIC CHARGE ESTIMATION OF A NEWBORN BLACK HOLE

2009 ◽  
Vol 18 (13) ◽  
pp. 2035-2045 ◽  
Author(s):  
ANTON BAUSHEV ◽  
PASCAL CHARDONNET
Keyword(s):  
Magnetic Field ◽  
Black Holes ◽  
Black Hole ◽  
Electric Charge ◽  
Charge Separation ◽  
Mass Ratio ◽  
Hole Formation ◽  
Upper Limit ◽  
Good Conductor ◽  
Charge Formula

Though a black hole can theoretically possess a very big charge ([Formula: see text]), the charge of the real astrophysical black holes is usually considered to be negligible. This supposition is based on the fact that an astrophysical black hole is always surrounded by some plasma, which is a very good conductor. However, it disregards the fact that black holes usually have some angular momentum, which can be interpreted as their rotation of a sort. If in the plasma surrounding the hole there is some magnetic field, it leads to electric field creation and, consequently, charge separation. In this article we estimate the upper limit of the electric charge of stellar mass astrophysical black holes. We have considered a new black hole formation process and shown that the charge of a newborn black hole can be significant (~ 1013 C ). Though the obtained charge of an astrophysical black hole is big, the charge-to-mass ratio is small, [Formula: see text], and it is not enough to affect significantly either the gravitational field of the star or the dynamics of its collapse.

scholarly journals Electrically-charged black holes and the Blandford-Znajek mechanism

2021 ◽  
Author(s):  
Serguei S Komissarov
Keyword(s):  
Magnetic Field ◽  
Black Holes ◽  
Black Hole ◽  
Electric Charge ◽  
Meissner Effect ◽  
Charged Black Holes ◽  
Field Lines ◽  
The One ◽  
Electrically Charged ◽  
The Magnetic Field

Abstract Recently, it was claimed by King & Pringle that accretion of electric charge by a black hole rotating in an aligned external magnetic field results in a “dead” vacuum magnetosphere, where the electric field is totally screened, no vacuum breakdown is possible, and the Blandford-Znajek mechanism cannot operate. Here we study in details the properties of the Wald solution for electrically charged black holes discussed in their paper. Our results show that the claim is erroneous as in the solution with the critical charge q0 = 2aB0 there exists a drop of electrostatic potential along all magnetic field lines except the one coinciding with the symmetry axis. It is also found that while uncharged rotating black holes expel external vacuum magnetic field from their event horizon (the Meissner effect), electric charging of black holes pulls the magnetic field lines back on it, resembling what has been observed in some previous force-free, RMHD and PIC simulations of black hole magnetospheres. This suggests that accretion of electric charge may indeed be a feature of the black hole electrodynamics. However, our analysis shows that the value q0 of the BH charge given by Wald is likely to be only an upper limit, and that the actual value depends of the details of the magnetospheric physics.

scholarly journals Feeding and feedback from little monsters: AGN in dwarf galaxies

2020 ◽  
Vol 15 (S359) ◽  
pp. 238-242
Author(s):  
Mar Mezcua
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Early Universe ◽  
Dwarf Galaxies ◽  
Scaling Relations ◽  
Strong Impact ◽  
Hole Formation ◽  
Intermediate Mass ◽  
Black Hole Formation ◽  
Low Mass

AbstractDetecting the seed black holes from which quasars formed is extremely challenging; however, those seeds that did not grow into supermassive should be found as intermediate-mass black holes (IMBHs) of 100 – 105 M⊙ in local dwarf galaxies. The use of deep multiwavelength surveys has revealed that a population of actively accreting IMBHs (low-mass AGN) exists in dwarf galaxies at least out to z ˜3. The black hole occupation fraction of these galaxies suggests that the early Universe seed black holes formed from direct collapse of gas, which is reinforced by the possible flattening of the black hole-galaxy scaling relations at the low-mass end. This scenario is however challenged by the finding that AGN feedback can have a strong impact on dwarf galaxies, which implies that low-mass AGN in dwarf galaxies might not be the untouched relics of the early seed black holes. This has important implications for seed black hole formation models.

scholarly journals Very High-Energy Emission from the Direct Vicinity of Rapidly Rotating Black Holes

Galaxies ◽  
2018 ◽  
Vol 6 (4) ◽  
pp. 122 ◽  
Author(s):  
Kouichi Hirotani
Keyword(s):  
Magnetic Field ◽  
Black Holes ◽  
Black Hole ◽  
Electric Field ◽  
Gamma Rays ◽  
Accretion Rate ◽  
High Energy ◽  
Relativistic Electrons ◽  
Field Lines ◽  
The Magnetic Field

When a black hole accretes plasmas at very low accretion rate, an advection-dominated accretion flow (ADAF) is formed. In an ADAF, relativistic electrons emit soft gamma-rays via Bremsstrahlung. Some MeV photons collide with each other to materialize as electron-positron pairs in the magnetosphere. Such pairs efficiently screen the electric field along the magnetic field lines, when the accretion rate is typically greater than 0.03–0.3% of the Eddington rate. However, when the accretion rate becomes smaller than this value, the number density of the created pairs becomes less than the rotationally induced Goldreich–Julian density. In such a charge-starved magnetosphere, an electric field arises along the magnetic field lines to accelerate charged leptons into ultra-relativistic energies, leading to an efficient TeV emission via an inverse-Compton (IC) process, spending a portion of the extracted hole’s rotational energy. In this review, we summarize the stationary lepton accelerator models in black hole magnetospheres. We apply the model to super-massive black holes and demonstrate that nearby low-luminosity active galactic nuclei are capable of emitting detectable gamma-rays between 0.1 and 30 TeV with the Cherenkov Telescope Array.

A ROBUST TEST OF GENERAL RELATIVITY IN SPACE

2007 ◽  
Vol 16 (12a) ◽  
pp. 2319-2324 ◽  
Author(s):  
JAMES GRABER
Keyword(s):  
Black Holes ◽  
General Relativity ◽  
Black Hole ◽  
Quadrupole Moment ◽  
Binary Systems ◽  
High Mass ◽  
Uniqueness Theorems ◽  
Mass Ratio ◽  
Intermediate Mass ◽  
Robust Test

LISA may make it possible to test the black-hole uniqueness theorems of general relativity, also called the no-hair theorems, by Ryan's method of detecting the quadrupole moment of a black hole using high-mass-ratio inspirals. This test can be performed more robustly by observing inspirals in earlier stages, where the simplifications used in making inspiral predictions by the perturbative and post-Newtonian methods are more nearly correct. Current concepts for future missions such as DECIGO and BBO would allow even more stringent tests by this same method. Recently discovered evidence supports the existence of intermediate-mass black holes (IMBHs). Inspirals of binary systems with one IMBH and one stellar-mass black hole would fall into the frequency band of proposed maximum sensitivity for DECIGO and BBO. This would enable us to perform the Ryan test more precisely and more robustly. We explain why tests based on observations earlier in the inspiral are more robust and provide preliminary estimates of possible optimal future observations.

scholarly journals Magnetized Particle Motion around Black Holes in Conformal Gravity: Can Magnetic Interaction Mimic Spin of Black Holes?

Universe ◽  
2020 ◽  
Vol 6 (3) ◽  
pp. 44 ◽  
Author(s):  
Kamoliddin Haydarov ◽  
Ahmadjon Abdujabbarov ◽  
Javlon Rayimbaev ◽  
Bobomurat Ahmedov
Keyword(s):  
Magnetic Field ◽  
Black Holes ◽  
Black Hole ◽  
Particle Motion ◽  
Center Of Mass ◽  
Conformal Gravity ◽  
Mass Energy ◽  
Particle Collisions ◽  
Center Of Mass Energy ◽  
Sgr A

Magnetized particle motion around black holes in conformal gravity immersed in asymptotically uniform magnetic field has been studied. We have also analyzed the behavior of magnetic fields near the horizon of the black hole in conformal gravity and shown that with the increase of conformal parameters L and N the value of angular component of magnetic field at the stellar surface decreases. The maximum value of the effective potential corresponding to circular motion of the magnetized particle increases with the increase of conformal parameters. It is shown that in all cases of neutral, charged and magnetized particle collisions in the black hole environment the center-of-mass energy decreases with the increase of conformal parameters L and N. In the case of the magnetized and negatively charged particle collisions, the innermost collision point with the maximum center-of-mass energy comes closer to the central object due to the effects of the parameters of the conformal gravity. We have applied the results to the real astrophysical scenario when a pulsar treated as a magnetized particle is orbiting the super massive black hole (SMBH) Sgr A* in the center of our galaxy in order to obtain the estimation of magnetized compact object’s orbital parameter. The possible detection of pulsar in Sgr A* close environment can provide constraints on black hole parameters. Here we have shown that there is degeneracy between spin of SMBH and ambient magnetic field and consequently the interaction of magnetic field ∼ 10 2 Gauss with magnetic moment of magnetized neutron star can in principle mimic spin of Kerr black holes up to 0.6 .

scholarly journals Black Component of Dark Matter

2014 ◽  
Vol 2014 ◽  
pp. 1-6 ◽  
Author(s):  
A. V. Grobov ◽  
S. G. Rubin ◽  
V. Yu. Shalamova
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Dark Matter ◽  
Mass Spectrum ◽  
Energy Density ◽  
Extra Dimensions ◽  
Primordial Black Hole ◽  
Hole Formation ◽  
Specific Mass ◽  
Black Hole Formation

A mechanism of primordial black hole formation with specific mass spectrum is discussed. It is shown that these black holes could contribute to the energy density of dark matter. Our approach is elaborated in the framework of universal extra dimensions.

scholarly journals Models of high-frequency quasi-periodic oscillations and black hole spin estimates in Galactic microquasars

2020 ◽  
Vol 643 ◽  
pp. A31
Author(s):  
A. Kotrlová ◽  
E. Šrámková ◽  
G. Török ◽  
K. Goluchová ◽  
J. Horák ◽  
...  
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Neutron Star ◽  
High Frequency ◽  
Accretion Disc ◽  
The Other ◽  
Periodic Oscillations ◽  
X Ray ◽  
Upper Limit ◽  
Oscillation Modes

We explore the influence of nongeodesic pressure forces present in an accretion disc on the frequencies of its axisymmetric and nonaxisymmetric epicyclic oscillation modes. We discuss its implications for models of high-frequency quasi-periodic oscillations (QPOs), which have been observed in the X-ray flux of accreting black holes (BHs) in the three Galactic microquasars, GRS 1915+105, GRO J1655−40, and XTE J1550−564. We focus on previously considered QPO models that deal with low-azimuthal-number epicyclic modes, |m| ≤ 2, and outline the consequences for the estimations of BH spin, a ∈ [0, 1]. For four out of six examined models, we find only small, rather insignificant changes compared to the geodesic case. For the other two models, on the other hand, there is a significant increase of the estimated upper limit on the spin. Regarding the falsifiability of the QPO models, we find that one particular model from the examined set is incompatible with the data. If the spectral spin estimates for the microquasars that point to a >  0.65 were fully confirmed, two more QPO models would be ruled out. Moreover, if two very different values of the spin, such as a ≈ 0.65 in GRO J1655−40 and a ≈ 1 in GRS 1915+105, were confirmed, all the models except one would remain unsupported by our results. Finally, we discuss the implications for a model that was recently proposed in the context of neutron star (NS) QPOs as a disc-oscillation-based modification of the relativistic precession model. This model provides overall better fits of the NS data and predicts more realistic values of the NS mass compared to the relativistic precession model. We conclude that it also implies a significantly higher upper limit on the microquasar’s BH spin (a ∼ 0.75 vs. a ∼ 0.55).

scholarly journals Accretion Disk Electrodynamics

1985 ◽  
Vol 107 ◽  
pp. 453-469 ◽  
Author(s):  
F. V. Coroniti
Keyword(s):  
Magnetic Field ◽  
Black Holes ◽  
Black Hole ◽  
Accretion Disk ◽  
Large Scale ◽  
Relativistic Jet ◽  
Scale Field ◽  
Magnetic Buoyancy ◽  
Large Scale Field ◽  
Viscous Transport

Accretion disk electrodynamic phenomenae are separable into two classes: 1) disks and coronae with turbulent magnetic fields; 2) disks and black holes which are connected to a large-scale external magnetic field. Turbulent fields may originate in an α - ω dynamo, provide anomalous viscous transport, and sustain an active corona by magnetic buoyancy. The large-scale field can extract energy and angular momentum from the disk and black hole, and be dynamically configured into a collimated relativistic jet.

scholarly journals 2.10. Self-similar viscous growth of the central core of AGN seeds

1998 ◽  
Vol 184 ◽  
pp. 77-78
Author(s):  
T. Tsuribe
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
The Self ◽  
Central Core ◽  
Viscous Effect ◽  
Hole Formation ◽  
Centrifugal Barrier ◽  
Massive Black Holes ◽  
Self Similar Solution ◽  
Self Similar

Dynamical collapse of rotating cloud and subsequent mass supply to the central object is the basic physical process on the formation of the central black holes in the high-z QSO cosmologically. Considering the formation of super massive black holes, the centrifugal barrier plays an important role. In this contribution, I consider the viscous effect to the self-gravitating disk which formed cosmologically. In particular, unsteady growth of the central core is treated consistently with surrounding accreting disks semi-analytically. A new self-similar solution of axisymmetric viscous accretion onto an evolving point mass is obtained. Application to QSO progenitor black hole formation is briefly discussed.

scholarly journals Relativistic Accretion into a Reissner-Nordström Black Hole Revisited

2012 ◽  
Vol 2012 ◽  
pp. 1-6 ◽  
Author(s):  
J. A. de Freitas Pacheco
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Flow Velocity ◽  
Critical Point ◽  
Event Horizon ◽  
Accretion Rate ◽  
Extreme Case ◽  
Mass Ratio ◽  
Relativistic Fluids ◽  
Sonic Point

The accretion of relativistic and nonrelativistic fluids into a Reissner-Nordström black hole is revisited. The position of the critical point, the flow velocity at this point, and the accretion rate are only slightly affected with respect to the Schwarzschild case when the fluid is nonrelativistic. On the contrary, relativistic fluids cross the critical point always subsonically. In this case, the sonic point is located near the event horizon, which is crossed by the fluid with a velocity less than the light speed. The accretion rate of relativistic fluids by a Reissner-Nordström black hole is reduced with respect to those estimated for uncharged black holes, being about 60% less for the extreme case (charge-to-mass ratio equal to one).

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